Parametric imaging of clear cell and papillary renal cell carcinoma using contrast-enhanced ultrasound (CEUS)

Abstract

PURPOSE: The aim of this study was to analyse clear cell and papillary renal cell carcinoma (RCC) examined with contrast-enhanced ultrasound (CEUS) and a second generation blood pool agent (SonoVue^®, Bracco, Milan, Italy) before clinical intervention.

MATERIALS AND METHODS: A total of 41 patients with histologically proven subtypes of RCC were examined. 29 patients had a clear cell RCC and 12 patients showed a papillary RCC. Average size in the clear cell RCC group was 6.07 cm and 1.88 cm in the papillary RCC group. An experienced radiologist examined all patients with CEUS. The following parameters were analysed: maximum signal intensity (PEAK), time elapsed until PEAK is reached (MTT), local blood flow (RBF), area under the time intensity curve (AUC) and the signal intensity (SI) during the course of time. For both groups all comparisons were made based on healthy renal parenchyma.

RESULTS: In the clear cell RCC significant differences (significance level p < 0.05) between cancerous tissue and the healthy renal parenchyma were noticed in all four parameters. The clear cell RCC showed a significant reduced blood volume. It reached the PEAK reading relatively rapidly and its signal intensity was always lower than that of the healthy renal parenchyma. In the arterial phase retarded absorption of the contrast agent was observed, followed by fast washing out of the contrast agent bubbles.

In the papillary RCC group, significant findings as to PEAK and RBF as well as a slightly significant difference as to AUC were recorded. The papillary RCC had a lower blood supply and reached its PEAK reading later. Its signal intensity was also reduced. The signal intensity of papillary NCC was significantly lower compared with clear cell RCC; absorption and washing out of the contrast agent was delayed.

CONCLUSION: CEUS seems to be an useful additional method to clinically differentiate between clear cell and papillary RCC. In daily clinical use, patients with contraindication for other imaging methods, especially the magnetic resonance imaging, might particularly benefit from this method.

1 Introduction

The clear cell renal cell carcinoma (clear cell RCC) has an incidence rate of 3% of all malign neoplasms and is on the third rank of the most common tumours of the urinary tract [1]. Europe has the highest incidence rate worldwide [2]. It occurs most commonly in patients aged between 60 and 70 and shows a gender distribution of 3:2 in favour of the female sex [3 , 24]. Letality is 40% within the first 5 years after initial diagnosis [10, 15]. Clear cell RCC is the sixth most common cause of all cancer-related causes of death and also shows the highest letality rate of tumours that originate from the urinary tract [9]. The incidence rate RCC increases by 2.5 % each year, which might be simply explained by better imaging quality and and regular screening programs. Radical nephrectomy is considered to be the only causal therapy with organ retaining or nephron sparing tumour surgery gaining more importance [19]. Therapy of choice is a clinical decision depending on factors such as histological subtyping, tumour size, existing metastases and accompanying illnesses [19]. In the current 2014 European guidelines, contrast-enhanced computer tomography (CE-CT) and magnetic resonance imaging (MRI) are recommended methods of medical imaging of the clear cell RCC. In special clinical cases, such as chronic renal failure of differing aetiology or known allergic reactions to contrast agents containing iodine or gadolinium, contrast-enhanced ultrasound (CEUS) is recommended as an alternative image modality option [17]. Contrary to CE-CT and MRI, the administered contrast agent in CEUS only remains intravascular, without affecting thyroid or renal function. Furthermore this technique uses a non iniozing radiation approach. In less than 0.002% of the cases, anaphylactic reactions by CEUS were described in literature [18, 21]. CEUS is already established as a fast, low-risk and cost effective way for the diagnosisof RCCs [5 , 11].

2 Materials and methods

Between June 2006 and June 2009 a total of 41 patients diagnosed with pathological renal changes were examined using CEUS. This study was approved by the local ethics committee. The study data were collected in compliance with the principles of the Helsinki/Edinburgh Declaration of 2002. Oral and written informed consent of all patients was obtained prior to each CEUS examination.

29 patients were diagnosed with clear cell RCC - three highly differentiated, 21 moderately and five mildly differentiated RCC –of an average size of 6.07 centimetres. 12 papillary RCC could be found - two highly differentiated and ten moderately differentiated RCC of an average size of 1.88 centimetres. Initially all patients had to give their prior oral and written consent. All patients were examined by the same experienced radiologist, who has more than 10 years of professional experience.

The CEUS examinations were all carried out with a Siemens (Germany) Acuson Sequoia 512 ultra sound device and a 4C1 curved array transducer. Additionally, contrast pulse sequencing (CPS) technology developed to detect the non-linear response of microbubbles, was used. A second generation blood pool contrast agent (SonoVue^®, Bracco, Milan, Italy) was administered through a peripheral 20–22 G needle in an antecubital vein followed by a flush of 5 to 10 ml of 0.9% saline solution (0.9% NaCl). 1.6 to 2.4 ml of contrast agent was administered in most cases and with a maximum of 4.8 ml or minimum of 1.0 ml according to the underlying condition. 1.0 ml of the contrast agent allows diagnostic views for approximately 3 minutes. After the administration of the contrast agent craniocaudal, transverse as well as longitudinal cine loops were acquired and stored in the picture archiving and communication system. Mean examination time was 3–5 minutes for the complete examination. We distinguished between an arterial and a venous phase. The arterial phase covered the first 10 to 30 seconds, the venous phase the first 30 to 45 seconds after the first microbubbles in the area to be examined could be detected. The gathered data were mathematically processed by Qontrast Esaote Sp (EC mark no 0051, class IIA). In order to keep accidental errors as low as possible, 3 tests in the carcinoma of each patient were carried out during the following periods:

When the first bubbles of the contrast agent flooded the tumour

30 seconds after administration of contrast agent

60 seconds after administration of contrast agent

120 Seconds after administration of contrast agent

Only the first three time intervals were considered relevant for statistical analysis, as images lasting more than 120 seconds have rarely been made of kidney tumours. Allocating the images to the particular time when they were taken was a further aspect. As CEUS is a real time examination and the quality of the images depends on the cooperation of the patient, the tissue to be examined was not always clearly visible. For this reason a divergence with respect to the timeline of no more than 12 seconds was mot avoidable.

The parameters examined for every time interval were as follows:

Peak reading: maximum signal intensity

Time to peak (TTP): time elapsed until maximum signal intensity is reached

Regional blood volume (RBV)

Regional blood flow (RBF)

Mean transit time (MTT)

Area under the curve (AUC)

RBV is proportional to the area under the time intensity curve (AUC). RBF represent the ration between RBV and MTT.

The parameters were automatically calculated according to formula based on the previously chosen gamma variate mode: SI (t) = PEAK*(t/TTP) (ß*TTP)e-ß*(t-TTP). Timing for the second measurement (TTP 2) was calculated based on both the measurement times as well as the assumption that the peak reading will be reached after 30 seconds (TTP 1). The parameter ß of the model could be approximated by means of the Newton method.

Three measurements were taken for every patient in the tumour as well as in the healthy renal parenchyma at each time interval and a mean value was calculated for each individual patient. The statistical analysis was based exclusively on the mean value at the respective period of time. To achieve this, 4 of the 5 parameters stated above were used, i. e. PEAK; AUC, MTT and RBF. These parameters provide essential information on the time of flooding, the retention period and the washing out of the contrast agent. The mean values were calculated for the tumour and the healthy tissue at each time interval. By means of a Monte-Carlo simulation, the area (AUC) under the respective gamma curve was approximated for each case. Mean Transit Time (MTT) is defined as the point in time when the area before and after relevant the point in time is halved. RBF represents the ratio of the AUC and the MTT. A paired t-test was used for the mean value divergence of the PEAK value of healthy tissue compared with tumour tissue. The statistical analysis was carried out by R (version 3.0.1). Bilaterally testing was done and a significance level of p = > 0.05 was determined [2].

3 Results

18 men and 11 women, aged on average 68.8 and 60.1 years respectively were included in the group with clear cell RCC. In native B-Mode sonography, the neoplasm were inhomogeneous and just under half of them (14/19) were hyperechoic. In 12 cases (12/29) the tumours were described as isoechoic and in three cases (3/29) as hypoechoic. The clear cell RCCs had an average size of 6.07 cm. In addition, a central necrosis was described in 10 tumours (Tables 1 and 2). Data collected during CEUS displayed significant differences in all four parameters. All statistical findings were based on the assumed level of significance of p > 0.05. A p value of 0.00 was calculated for the parameters PEAK, AUC and RBF and 0.02 for MTT accordingly (Figs. 1–4). According to these findings, the clear cell RCC stands out because of its reduced blood volume. However, it reaches the PEAK value relatively rapidly. Therefore the clear cell RCC shows weaker signal intensity than the surrounding healthy renal parenchyma over the whole period.

10 men and 2 women aged on average 72.5 and 62.5 years respectively were examined in the group with papillary renal cell carcinoma. In native B-mode sonography the tumours were inhomogeneous and had an average size of 1.88 cm. Half of them (6/12) were described as isoechoic, 2/12 were hyperechoic and 3/12 hypoechoic. One further tumour had a hyperechoic periphery and a hypoechoic centre (Tables 1 and 2).

A central necrosis could be described in three cases only. The statistical findings showed significant differences for the following parameters: PEAK with a p-value of p = >0.001, RBF with a p-value of 0.01 and a slightly significant difference for AUC with a p-value of 0.09. For MTT a non-significant difference of 0.50 (Figs. 1–4) was calculated. It can be concluded from these findings that blood supply in the papillary RCC is lower and the PEAK value in the tumour is reached during the later phase. The papillary RCC also showed retarded absorption of the contrast agent and a faster washing out of the contrast agent. In consequence, the papillary RCC showed lower signal intensity (SI) than the healthy renal parenchyma over the whole period.

4 Discussion

The correlation between dignity of a renal tumor and its reaction to CEUS is studied since several years. Chiba observed how microbubbles absorb contrast agents in renal tumours and compared these findings with color Doppler [2]. The author stated that small renal tumours can be successfully detected and diagnosed with CEUS. Ascenti et al. examined hyperechoic renal tumours with color Doppler and the first generation contrast agent Levovist^® assuming the benefit of Levovist^® in differential diagnosis of pseudotumors and neoplasm [1]. Clinical use of CEUS can be increasingly observed and studies suggest a possible positive correlation between the dignity of the tumour and the diverse reaction to contrast agents. This is also the aim of this study.

In this study, the most frequent malign renal tumours were quantitatively examined and compared based on parameters gathered with the help of CEUS.

Clear distinctions with respect to PEAK, AUC, MTT and RBF in the largest group of malign renal tumours, i. e. the group of clear cell RCC with a total of 29 cases could be made. Compared with the healthy renal parenchyma, the clear cell RCC showed a reduced blood volume. One possible explanation for this finding could be the frequently existing haemorrhages and necroses that could be described in 10 out of 29 patients. At the same time, there was minimal difference in the PEAK value suggesting an increased metabolism of the tumour cells. The clear cell RCC featured a retarded absorption of the contrast agent during the early phase and a faster wash-out during the later phase. The retarded absorption of the contrast agent might be explained by the lower rate of small calibre blood vessels. The faster washing out would be possible in arteriovenous fistulas or in normal physiological reflux through the renal vein [23]. Throughout this period of time, this type of tumour showed lower signal intensity than healthy renal parenchyma presenting the clear cell RCC as heterogeneous and hypoechoic compared with the surrounding tissue.

12 cases of patients with papillary RCC were examined this study. Compared with healthy renal parenchyma, significant findings were made for PEAK and RBF (Figs. 1 and 4). The readings suggest a reduced blood supply of the RCC, which had a significantly lower PEAK reading than healthy renal cell parenchyma. The papillary RCC featured significantly reduced signal intensity over the whole period. This may be due to a significantly retarded absorption of the contrast agent during the early phase and a faster wash-out during the later phase.

The findings suggest that clear cell and papillary RCC react to contrast agent in a different way. Compared with the signal intensity of healthy renal parenchyma, the signal intensity of the clear cell RCC records an almost synchronic progression compared with the significantly reduced signal intensity of the papillary renal cell carcinoma. It is therefore possible to conclude that the papillary RCC is more hypoechoic than the clear cell RCC. Furthermore, the significantly higher PEAK value of the clear cell RCC (Fig. 1) supports this observation. Both, more rapid absorption and washing out of the contrast agent bubbles happen in the clear cell RCC compared with the papillary RCC. Although Figs. 2 and 4 shows a lower reading for AUC and RBF in the clear cell RCC group compared with the papillary RCC group, it is possible to explain this by the fact that the average tumour size of the RCC is significantly larger. Measurements made near existing haemorrhage and necrotic areas influence the statistical analysis regarding blood perfusion. Nevertheless first conclusions about the vascular supply and the histological set-up of malign RCC can be drawn by their reaction to contrast agent in CEUS.

Fan et al. examined malign and benign renal tumours with a diameter of no more than five centimetres with CEUS [25]. The authors conclude that the inhomogeneous and hyperechoic image during the late phase is more significant for diagnosing RCC (Specificity 100%, sensitivity 59.1%). Contrary to what is stated in the current study, with tumour sizes no larger than 11.5 centimetres and representing a limited factor during the measurements, the authors observe a more highly enhanced signal in a larger number of clear cell RCC with a diameter of no more than five centimetres. At the same time, they describe a reduced absorption of the contrast agent in the papillary RCC, which corresponds to the current findings.

Dong et al. described how differently clear cell RCC react to contrast agents [7]. The variables analysed in their study are TTP and AUC. Our study showed a different behaviour pattern of the clear cell RCC: i.e. slow flooding and fast washing out.

Contrary to the present study, Xu et al. observed that the contrast agent is absorbed differently, i. e. in increased or equal quantities by the majority of the clear cell RCC [25].

Li et al. also showed in their study an increased signal intensity during the early phase as typical characteristics of the clear cell RCC [16]. Contrary to these findings the papillary and chromophobe RCC are characterized by a lower absorption of the contrast agent and are less heterogeneous in the early phase. Slow washing in and fast washing out can also be observed as a pattern in this case.

Ignee et al. showed that the majority of the RCC show an increased signal intensity in the early phase (up to the 30th second) [14]. In addition the reaction to the contrast agent in the arterial phase is different from that in the late phase, in which two thirds of the lesions show reduced signal intensity. Furthermore the authors report hypervascularity in the majority of the clear cell RCC and hypovascularity in a third of the papillary RCC.

Based on our findings, this study suggests a new hypothesis how renal tumours react to contrast agents. For both histopathology and the diverse ranges of application, better understanding of CEUS allows new possibilities in daily clinical routine. This procedure allows risk patients to be examined fast and precisely. Tay et al. who used CEUS on patients with RCC also draw this conclusion [20].

Ignee et al. reported their clinical experience with CEUS of a 39 year-old patient who had previously received two kidney transplants following the need for dialysis and rapidly progressing glomerulonephritis after an abortion. Through CEUS they were able to diagnose a papillary RCC in the young patient, who fully recovered after resection of the tumour [13].

Clevert et al. reported a similar case of a 37 year-old patient diagnosed with a papillary RCC using CEUS despite insufficient CT and MRT findings. There were no postoperative complications is this case either [4].

5 Conclusion

This study confirms the relevance of CEUS as an essential additional diagnostic tool. This relatively new method offers manifold ways of diagnosis and future oncological therapy. Establishing CEUS in clinical routine allows fast, correct, low-risk and cost-effective examinations. In daily clinical use, patients with contraindication for other imaging modalities, especially the magnetic resonance imaging, might particularly benefit from this method.

References

Ascenti

, Zimbaro

, Mazziotti

, Gaeta

, Settineri

and Scribano

, Usefulness of power Doppler and contrast-enhanced sonography in the differentiation of hyperechoic renal masses, Abdom Imaging 26 (2001), 654–660.

Chiba

, Enhanced ultrasonography in the diagnosis of renal tumors, Nihon Rinsho 56 (1998), 1030–1034.

Chow

W.H.

, Devesa

S.S.

, Warren

J.L.

and Fraumeni

J.F.

Jr , Rising incidence of renal cell cancer in the United States, JAMA: The Journal of the American Medical Association 281 (1999), 1628–1631.

Clevert

D.A.

, Bensler

, Stickel

, Horng

, Strautz

, Flach

, et al., Contrast enhanced ultrasound eases interpretation of an unclear renal tumor in addition to CT, MRI and histological findings–a case report in a young patient, Clin Hemorheol Microcirc 36 (2007), 313–318.

Clevert

D.A.

, Sterzik

, Braunagel

, Notohamiprodjo

and Graser

, Modern imaging of kidney tumors, Der Urologe Ausg A 52 (2013), 515–526.

Decastro

G.J.

and McKiernan

J.M.

, Epidemiology, clinical staging, and presentation of renal cell carcinoma, Urol Clin North Am 35 (2008), 581–592; vi.

Dong

X.Q.

, Shen

, Xu

L.W.

, Xu

C.M.

, Bi

and Wang

X.M.

, Contrast-enhanced ultrasound for detection and diagnosis of renal clear cell carcinoma, Chin Med J (Engl) 122 (2009), 1179–1183.

Escudier

, Porta

, Schmidinger

, Algaba

, Patard

J.J.

, Khoo

, et al., Renal cell carcinoma: ESMO Clinical Practice Guidelines for diagnosis, treatment and follow-up, Annals of Oncology: Official Journal of the European Society for Medical Oncology / ESMO 25(Suppl 3) (2014), iii49–iii56.

Godley

P.A.

and Ataga

K.I.

, Renal cell carcinoma, Curr Opin Oncol 12 (2000), 260–264.

10.

Greenlee

R.T.

, Murray

, Bolden

and Wingo

P.A.

, Cancer statistics, CA Cancer J Clin 50 (2000), 7–33.

11.

Greis

, Technical aspects of contrast-enhanced ultrasound (CEUS) examinations: Tips and tricks, Clin Hemorheol Microcirc 58 (2014), 89–95.

12.

Hock

L.M.

, Lynch

and Balaji

K.C.

, Increasing incidence of all stages of kidney cancer in the last 2 decades in the United States: An analysis of surveillance, epidemiology and end results program data, The Journal of Urology 167 (2002), 57–60.

13.

Ignee

, Hocke

, Selbach

, Cui

X.W.

, Woenckhaus

and Dietrich

C.F.

, Papillary renal cell carcinoma in the transplanted kidney - a case report focusing on contrast enhanced ultrasound features, Med Ultrason 14 (2012), 246–250.

14.

Ignee

, Straub

, Brix

, Schuessler

, Ott

and Dietrich

C.F.

, The value of contrast enhanced ultrasound (CEUS) in the characterisation of patients with renal masses, Clin Hemorheol Microcirc 46 (2010), 275–290.

15.

Landis

S.H.

, Murray

, Bolden

and Wingo

P.A.

, Cancer statistics, CA Cancer J Clin 49 (1999), 8–31. 1.

16.

, Liang

, Guo

, Yu

, Cheng

, et al., Real-time contrast-enhanced ultrasound in diagnosis of solid renal lesions, Discovery Medicine 16 (2013), 15–25.

17.

Ljungberg

, Bensalah

, Canfield

, Dabestani

, Hofmann

, Hora

, et al., EAU guidelines on renal cell carcinoma: update, European Urology 67 (2015), 913–924.

18.

Piscaglia

and Bolondi

, Italian Society for Ultrasound in M, Biology Study Group on Ultrasound Contrast A, The safety of Sonovue in abdominal applications: Retrospective analysis of 8 investigations, Ultrasound in Medicine & Biology 32 (2006), 1369–1375.

19.

Tannir

N.M.

, Renal cell carcinoma. Oxford: Oxford University Press; 2014.

20.

Tay

K.J.

, Ho

H.S.

, Low

A.S.

and Cheng

C.W.

, Is contrast enhanced ultrasound a valid alternative diagnostic modality for renal cell carcinoma in patients with renal impairment? Ann Acad Med Singapore 41 (2012), 127–128.

21.

Ter Haar

, Safety and bio-effects of ultrasound contrast agents, Med Biol Eng Comput 47 (2009), 893–900.

22.

Wallen

E.M.

, Pruthi

R.S.

, Joyce

G.F.

and Wise

, Urologic Diseases in America P. Kidney cancer, The Journal of Urology 177 (2006), 2006–2018; discussion 18-9.

23.

Wei

, Fu

, Yao

, Liu

and Yang

, Two- and three-dimensional contrast-enhanced sonography for assessment of renal tumor vasculature: Preliminary observations, J Ultrasound Med 32 (2013), 429–437.

24.

Woldrich

J.M.

, Mallin

, Ritchey

, Carroll

P.R.

and Kane

C.J.

, Sex differences in renal cell cancer presentation and survival: An analysis of the National Cancer Database, The Journal of Urology 179 (2008), 1709–1713; discussion 13.

25.

Z.F.

, Xu

H.X.

, Xie

X.Y.

, Liu

G.J.

, Zheng

Y.L.

, Liang

J.Y.

, et al., Renal cell carcinoma: Real-time contrast-enhanced ultrasound findings, Abdom Imaging 35 (2010), 750–756.